1. Field of the Invention
The present invention relates to a method of producing semiconductor devices and an etching liquid used in this production.
2. Description of Related Art
In recent years progress has been made in device refinement, and gate wiring resistance, parasitic resistance of the source drain part of transistors, and contact resistance have risen accordingly. Therefore, there is a problem with conventional devices in that the high-speed operation that is anticipated based on a scaled model cannot actually be realized.
As a result, silicide (self-alignment silicide) technology is used with which silicide film of a metal with a high melting point is formed in self-aligning manner on the gate and diffusion layer regions to realize a reduction in sheet resistance. In particular, titanium silicide (TiSi2) and cobalt silicide (CoSi2) are used because of low resistance and thermal stability.
When titanium silicide is used there is a problem with the fine line effect in that it becomes difficult to reduce resistance due to inhibition of phase transition from the C49-phase titanium silicide of high resistance (C49-TiSi2) to the C54 phase of low resistance (C54-TiSi2) when titanium silicide is formed on a fine pattern. Moreover, it is a known fact that there is a dramatic increase in sheet resistance of titanium silicide due to aggregation of titanium silicide and disconnection of the silicide layer when lines are as fine as 0.1 μm. Consequently, it is necessary to control the fine line effect and aggregation of titanium silicide when titanium silicide is used.
When cobalt silicide is used, there is none of the fine line effect that is generated when titanium silicide is used. In particular, it is reported in IEDM Tech Dig., p 449, 1995 that a reduction in resistance with up to fine lines of 0.075 μm can be realized by forming titanium nitride film as the cap film on the top surface of cobalt and thereby inhibiting oxidation of the cobalt surface with this cap film.
Therefore, it appears that cobalt salicide technology using titanium nitride cap film is useful for the formation of fine devices of 0.1 μm.
A conventional method of producing semiconductor devices using cobalt salicide technology will be described below while referring to FIG. 3. FIGS. 3(A) through (F) are a flow chart that explains the production processes of this conventional technology. Each figure is a cross section of the semiconductor device.
First, as shown in FIG. 3(A), diffusion layer 102 and field insulation film 104 are formed on the surface region on the top of substrate 100, while gate insulation film 106 is formed on the top of substrate 100 and gate electrode 108 is formed on the top of gate insulation film 106. Side walls 109 are then set up as usual.
Next, as shown in FIG. 3(B), cobalt film 110 is formed so that it covers substrate 100, diffusion layer 102, field insulation film 104, gate insulation film 106, gate electrode 108, and side walls 109 and titanium nitride film 112 is formed as cap film so that it covers the top of cobalt film 110.
Next, as shown in FIG. 3(C), cobalt film 110 adjoining diffusion layer 102 and diffusion layer 102 and cobalt film 110 adjoining gate electrode 108 and gate electrode 108 are each reacted by RTA (rapid thermal annealing) at a temperature within a temperature range of 450° C. to 600° C. to form CoSi layers 114a, 114b and 116. This RTA treatment serves as the first RTA.
Then, as shown in FIG. 3(D), titanium nitride film 112 is removed using an ammonia-hydrogen peroxide-water mixture.
Next, as shown in FIG. 3(E), unreacted cobalt film 110 is removed using a sulfuric acid-hydrogen peroxide-water mixture (H2SO4—H2O2 (sulfuric acid hydrogen peroxide mixture)) or hydrochloric acid-hydrogen peroxide-water mixture (HCl—H2O2—H2O).
Finally, as shown in FIG. 3(F), CoSi layers 114a, 114b, and 116 are reacted by performing RTA at a temperature within a temperature range of 750° C. to 900° C. to form CoSi2 layers 114a′, 114b′, and 116′. This RTA treatment serves as the second RTA.
It has been confirmed by SEM (scanning electron microscope) observation of CoSi2 layer parts 114a′, 114b′, and 116′ that the edges of the CoSi2 layers have been worn away in semiconductor devices produced using prior art.
FIG. 4 is a typical example of the edges of the CoSi2 from SEM observation. Moreover, FIG. 4 is an enlargement of the main parts of the figure during process (F) in FIG. 3. The dotted line ‘a’ shows the part where edges have been worn away by the above-mentioned etching.
There are problems when the CoSi2 is worn away in this manner in that CoSi2 sheet resistance increases and the fluctuations in resistance become larger, etc. The reason for this is that when titanium nitride film is removed with an ammonia-hydrogen peroxide-water mixture, the film is etched up to the CoSi layer, which is on the bottom of the titanium nitride film, and as a result, the CoSi film becomes thinner, and the CoSi2 film that is then formed by the second RTA treatment becomes even thinner.